Device for the precipitation of layers of semiconductor material

ABSTRACT

Epitaxial device in which semiconductor wafers to be coated are disposed at the bottom of a vertical cylindrical reaction vessel and are heated to the high temperature required for precipitation by a heat source arranged underneath the bottom. Fresh reaction gas is fed to the heated semiconductor wafers from above and the spent gas is removed again upwards through holes arranged along an annular zone in the wall of the reaction vessel. The spent gas then passes to two exhaust chambers connected in series. The flow resistance of the gas discharge being essentially determined by the flow resistance between the two exhaust chambers.

United States Patent [191 Sussmann [54] DEVICE FOR TIIE PRECIPITATION orLAYERS or SEMICONDUCTOR MATERIAL [75] Inventor:' Erhard 'Sussmann,Poing, Germany [73] Assignee: Siemens Aktiengesellschaft Munich;

Berlin, Erlangen, Germany 22 Filed: on. 29, 1971 211 Appl.No.:193,743

47, 50, 50.1, 326, DIG. 5, 429

[56] References Cited UNITED STATES PATENTS 2,884,894 5/1959 Ruppertetal..1l8/48 1 May 29,1973

Primary Examiner-Morris Kaplan Attorney-Arthur E. Wilford, Herbert L.Lerner and Daniel J. Tick [5 7 ABSTRACT Epitaxial device in whichsemiconductor wafers to be coated are disposed at the bottom of avertical cylindrical reaction vessel and are heated to the hightemperature required for precipitation by a heat source arrangedunderneath the bottom. Fresh reaction gas is fed to the heatedsemiconductorvwafers from above and the spent gas is removed againupwards through holes arranged along an annular zone in the wall of thereaction vessel. The spent gas then passes to two exhaust chambersconnected in series. The flow resistance of the gas discharge beingessentially determined by the flow resistance between the two exhaustchambers.

18 Claims, 1 Drawing Figure DEVICE FQR THE PRECIPITATION 01F LAYERS FSEMICONDUCTOR MATE 1 The present invention relates to a device for theprecipitation of layers of semiconductor material, particularly ofmonocrystalline material, from an appropriate reaction gas on thesurface of semiconductor wafers disposed at the bottom of a verticalcylindrical reaction vessel and heated by a heat source arrangedunderneath the bottom to the high temperature required forprecipitation. Fresh reaction gas is fed to the heated semiconductorwafers via a feed tube which extends into the reaction space of thereaction vessel from above and which, in particular, is swivable. Thespent reaction gas upwardly leaves the semiconductor wafers to bedoated.

Such devices have been described, for instance, in U.S. Pat. Nos.3,472,684; 3,486,933. All of these publications describe a method forthe preparation of layer of monocrystalline semiconductor material,particularly silicon, wherein an arrangement of the type described aboveis used. Experience has shown that particularly uniform epitaxial layersare obtained by such devices. in the course of testing such devices andthe methods described in the above-cited publications, it has beenfound, however, that in spite of all the precautions certainnonuniformities of the layers occur. These nonuniformities are caused bya certain unidirectionality of the gas flow. As was recognized accordingto the invention, these nonuniformities in the gas flow must beattributed to the manner in which the spent reaction gas'is removed inthe known devices. It is an object of the invention to achieve animprovement also in this respect.

This is achieved, according to the invention, using the above-describeddevice for the precipitation of layers of semiconductor material from anappropriate reaction gas on the surface of semiconductor wafers byproviding an exhaust arrangement for the spent reac tion gas from thereaction space of the reaction vessel consisting of two annular exhaustchambers which are disposed concentrically with respect to each otherand to the vertical cylindrical reaction space. The exhaust chamberswith respect to the flow of the spent reaction gas, are connected inseries with corresponding openings in the wall between the reactionspace and the inner exhaust chamber and the wall betweenthe two exhaustchambers, as well as of a gas venting tube connected to the outerexhaust chamber. The openings leading from the reaction space into theinner exhaust chamber are arranged above the mouth of the feed tube forthe fresh reaction gas into the reaction space and above the connectingopenings between the two concentric exhaust chambers. The total flowresistance of the openings between the reaction space and the innerexhaust chamber is adjusted to be smaller than the total flow resistanceof the openings between the two concentric exhaust-chambers.

According to a further feature of the invention, an important feature ofthis device consists in the fact that the openings between the reactionspace and the inner exhaust chamber, as well as the openings between thetwo exhaust chambers, are made in the corresponding walls along theazimuthal ring zone respectively and are arranged within the individualring zones at equal spacings from each other.

Experience leading to the invention has shown that the danger of anundesired precipitation of semiconductor material at the feed lines andat the wall of the reaction vessel increases with increases in flowvelocity of the reaction gas. The danger is particularly great at theconstrictions of the gas exhaust openings. For this reason, the acutedanger of undesirable precipitation leading to disturbing nuclei existsat the exit points if the latter are arranged, as for instance, in thearrangement according to the aforementioned patents or U. S. Pat. Nos.3,505,499; 3,519,798 and 3,536,892, in the lid of the cylindricalreaction vessel. The attempt, apparent in the U.S. Pat. No. 3,486,933,to prevent this by a screen has been found to be unsatisfactory as tothe gas flow in the reaction space and therefore as the uniformity ofthe supply and removal of the reaction gas with occurrence of unstableback phenomena.

According to the invention, the exhaust gas, upon leaving the reactionspace, encounters at first no appreciable flow resistance. The latteroccurs rather only inthe transition from the inner exhaust chamber tothe outer exhaust chamber. There the danger of undesired precipitationis greatest. However, this point is located outside of the reactionspace proper, so that disturbing or defect nuclei produced there cannotfall on the semiconductor wafers to be coated, which are situated at thebottom of the reaction vessel. A uniform distribution of the dischargeopenings from the reaction space, especially their design as anazimuthal horizontal annular slot, interrupted by at most a fewequidistant spacers, results in a uniform exhaust of the spent gas intothe inner exhaust chamber. It is important for uniform exhaust that alsothe openings, between the two exhaust chambers, having the higher flowresistance are uniformly distributed along a annular or ring shaped zonein the wall between the two exhaust chambers. The gas venting tubeopening into the outer exhaust chamber, however, is not critical. Anadjustable valve arranged in it permits more or less flow of thedischarged gases, as required. The total flow resistance of thedischarge point for the spent reaction gas should be such that the gasbetween the two exhaust chambers encounters a substantially larger,about 20 to times larger, flow resistance than in the transition from.the reaction space to the inner exhaust chamber. However, it depends ineach case on the desired reaction conditions, particularly also on thedesired dwell time of the reaction gas in the reaction space, whetherthe total flow resistance of the gas discharge is adjusted to be largeor small. The already mentioned valve for adjusting the dischargeresistance in the gas venting tube, which is suitably made wide, fromthe outer exhaust chamber represents a simple adjustment means, so thatit is recommended to make the flow resistance from the reaction space tothe outer exhaust chamber not too large.

The arrangement is appropriately operated observing the considerationsthat have already been set forth in U. S. Pat. Nos. 3,505499; 3,519,798and 3,536,892. The pressure of the inflowing reaction gas is chosen inthe feed tube in such a manner that the reaction gas reaches thesemiconductor wafers disposed at the bottom of the reaction vessel withcertainty in spite of the resistance of the exhaust gas. Accordingly, itis reccommend here that the fresh reaction gas enter the reaction spacewith a Reynolds number of at most 50, or in particular, at most 40. Itis further recommendedthat the gas feeding tube is swivable so that thepoint of entry of the fresh reaction gas is along a path running abovethe semiconductor wafers to be coated and which is adapted to theperiphery of the total precipitation area given by the totality of thesemiconductor wafers present, exhibiting radial symmetry with respect toits center, in such a manner that the image generated by orthogonalprojection of the point of entry on the total precipitation area along apath on the total precipitation area becomes slower the further therespective point of the trajectory is removed from the center of thetotal precipitation area. Furthermore, points of the image path havingthe same radial distance from the center of the total precipitationarea, are traversed by the image with equal frequency, as counted overthe the total precipitation time.

The invention is illustrated and described hereinbelow. It is notintended to be limited to the details shown, since various modificationsmay be made therein within the scope and the range of the claims. Theinvention, however, together with additional objects and advantages willbe best understood from the following desciption and in connection withthe accompanying Drawing, in which:

The Drawing shows a preferred embodiment of the invention.

The cylindrical reaction space 1 is closed off at the bottom by acup-shaped lower part 2, and by a cylindrical upper part 3. These partsconsist practically of quartz. The reaction space is closed at the topby a lid 4, for instance, of alloy steel. The feed tube 9, for the freshreaction gas, is brought through this lid. A viewingwindow 12, forpyrometrically measuring the temperature at the semiconductor wafers tobe coated, is

also fitted into lid 4. I

The wafers to be coated 5, are disposed at the bottom of the cup-shapedlower part 2. The wafers are heated from below via heat equalizing plate7, the heat being supplied by a heating element 6, through which currentflows. The lower part 2 of the reaction space 1 and the heating device6, 7 are appropriately located in a cooled casing metal 8.

The fresh reaction gas is supplied via the gas feeding tube 9 whichpenetrates the metal lid 4. It is desirable that the tube is swivable inthe lid. The appropriate seals 11, which prevent the reaction gas fromescaping at the feed through point, of course, must be chemicallyandthermally resistant, resilient material. Reference can be made to theabove-mentioned patents, regarding the detailed design of the gas entrypoint 9.

As will be seen from the Figure, the lid 4 extends all around beyond thewall 3 of the cylindrical reaction vessel. From its periphery an annularwall 13 extends downward, which forms the outer boundary of the outerannular exhaust chamber 14. Gas discharge tube 23 is in this wall 13. Asecond annular wall extends further inward and is tightly connected, onthe one hand, with the lid 4, and on the other hand, at its lower edge,with the already mentioned wall 13. In this manner the outer exhaustchamber 14 is formed. The wall 15 contains a number of evenly spacedholes 16, which form the connection between the interior of the outerexhaust chamber 14 and the inner exhaust chamber 17 which is arrangedbetween the wall 15 and the wall 3 of the reaction space 1. It is alsohermetically sealed against the outer space by appropriate wall partsand has only one connection to the outer exhaust chamber 14 and thereaction space 1.

The connection between the reaction space 1 and the inner, annularexhaust chamber 17 is situated directly below the lid 4. It consists ofone or several azimuthal slots 18, the total flow resistance of which isconsiderably smaller compared to that of the openings 16, at least by afactor of one-fifth and preferably onetwentieth or one-hundredth. All ofthe openings 18 and the openings 16, respectively, have the same shapeand dimensions.

The larger flow resistance between the two exhaust chambers, as comparedto that between the inner exhaust chamber and the reaction space can beachieved, on the one hand, by making the openings 18 correspondinglylarger than the openings 16 and/or by providing correspondingly moreopenings 18 as compared to the openings 16. The arrangement of theopenings 18 immediately below the lid 4 ensures the no dead spaces areformed in the reaction space with respect to the gas flow. In any event,the openings 18 must be arranged above the entry point for the freshreaction gas, i.e., the mouth of the gas feeding tube 9. Similarly, theopenings 18 must be arranged above the openings 16, so that the spentreaction gas flowing in the chamber 17 must flow somewhat downward.

What is claimed is:

1. In a device for the precipitation of layers of semiconductor materialfrom an appropriate reaction gas on the surface of semiconductor waferswhich are disposed at the bottom of a vertical cylindrical reactionvessel and are heated to the high temperature required for precipitationby a heat source arranged underneath the bottom, in which the freshreaction gas is fed to the heated semiconductor wafers via swivable feedtube which extends into the reaction space of the reaction vessel fromabove and the spent reaction gas leaves the semiconductor wafers to becoated in an upward direction, the improvement which comprises anexhaust system for the spent reaction gas from the reaction spaceconsisting of two annular exhaust chambers which are disposedconcentrically with respect to each other and to the verticalcylindrical reaction space with a common wall between the inner of saidtwo annular exhaust chambers and said reaction space and a common wallbetween the outer of said two exhaust chambers and said inner exhaustchamber, said exhaust chambers are connected in series as to the flow ofthe spent reaction gas via openings in the wall between the reactionspace and the inner exhaust chamber and the wall between the two exhaustchambers and a gas venting tube connected to the outer exhaust chamber,the openings leading from the reaction space to the inner exhaustchamber are arranged above the mouth of the tube feeding fresh reactiongas into the reaction space and above the connecting openings betweenthe two concentric exhaust chambers, the total flow resistance of theopenings between the reaction space and the inner exhaust chamber isless than the total flow resistance of the openings between the twoconcentric exhaust chambers.

2. The device of claim 1, wherein the openings between the reactionspace and the inner exhaust chamber and the openings between the twoexhaust chambers are arranged in the corresponding walls along arespective azimuthal ring zone.

3. The device of claim 1, wherein the openings between the reactionspace and the inner exhaust chamber and the openings from the innerexhaust chamber each have the same dimensionsand are arranged at equalspacings with respect to each other.

4. The device of claim 1, wherein the number of the openings between thereaction space and the inner exhaust chamber is larger than the numberof openings between the two exhaust chambers.

5. The device of claim 3, wherein the individual openings between thereaction space and the inner exhaust chamber are larger than theindividual openings between the two exhaust chambers.

6. The device of claim 1, wherein the total flow resistance for thespent reaction gas between the two exhaust chambers is adjusted to belarger by a factor of at least 5 than the flow resistance between thereaction space and the inner exhaust chamber.

7. The device of claim 1, wherein the total flow resistance for thespent reaction gas between the two exhaust chambers is adjusted to belarger by a factor of at least 20 to 100, than the flow resistancebetween the reaction space and the inner exhaust chamber.

8. The device of claim 1, wherein the flow resistance in the gas ventingtube for gas leaving the outer exhaust chamber is controllable by avalve and that the flow resitance with the valve open is so small thatthe total flow resistance is practically set by the flow resistancebetween the two exhaust chambers.

9. The device of claim 1, wherein the openings between the reactionspace and the inner exhaust chamberare horizontal slots which complementeach other to form a horizontal annular slot interrupted only by localspacers between a lid of the reaction vessel and the upper edge of thecylindrical wall of the reaction space.

10. The device of claim 9, wherein the openings between the reactionspace and the inner exhaust chamber are arrangeddirectly at the upperend of the reaction space.

11. The device of claim 9, wherein both concentric and annular exhaustchambers are closed on top by a lid on the reaction vessel, said lidextending radially beyond the wall of the reaction vessel.

12. The device of claim 11, wherein the outer exhaust chamber is formedby two annular walls which extend downward from the lid of the reactionvessel and are arranged concentrically with respect to each other and tothe reaction space, said walls being hermetically connected with eachother, a gas venting tube attached at the outer wall and connectingopenings in the inner wall connecting to the inner exhaust chamber.

13. The device of claim 12, wherein the wall of the reaction spaceconsists of quartz and the lid of the reaction vessel consists of metal.

14. The device of claim 12, wherein the wall of the reaction spaceconsists of glass and the lid of the reaction vessel consists of alloysteel.

15. The device of claim 12, wherein the walls of the outer exhaustchamber consists of the same material as the lid of the reaction vessle.

16. The device of claim 12, wherein the inner exhaust chamber formed bythe inner wall of the outer exhaust chamber and the wall of the reactionspace is sealed toward the bottom by a sealing ring of thermally andchamically resistant, resilient material.

17. The device of claim 16 wherein the sealing ring is pressed by meansof a metal washer from the outside against the wall of the reactionspace and against the inner wall of the outer exhaust chamber, saidwasher being tightened against the lower edge of the wall of the outerexhaust chamber by means of a mounting and clamping device. I

18. The device of claim ll,-wherein a quartz glass viewing window isdisposed in the lid'of the reaction vessel.

1. In a device for the precipitation of layers of semiconductor materialfrom an appropriate reaction gas on the surface of semiconductor waferswhich are disposed at the bottom of a vertical cylindrical reactionvessel and are heated to the high temperature required for precipitationby a heat source arranged underneath the bottom, in which the freshreaction gas is fed to the heated semiconductor wafers via swivable feedtube which extends into the reaction space of the reaction vessel fromabove and the spent reaction gas leaves the semiconductor wafers to becoated in an upward direction, the improvement which comprises anexhaust system for the spent reaction gas from the reaction spaceconsisting of two annular exhaust chambers which are disposedconcentrically with respect to each other and to the verticalcylindrical reaction space with a common wall between the inner of saidtwo annular exhaust chambers and said reaction space and a common wallbetween the outer of said two exhaust chambers and said inner exhaustchamber, said exhaust chambers are connected in series as to the flow ofthe spent reaction gas via openings in the wall between the reactionspace and the inner exhaust chamber and the wall between the two exhaustchambers and a gas venting tube connected to the outer exhaust chamber,the openings leading from the reaction space to the inner exhaustchamber are arranged above the mouth of the tube feeding fresh reactiongas into the reaction space and above the connecting openings betweenthe two concentric exhaust chambers, the total flow resistance of theopenings between the reaction space and the inner exhaust chamber isless than the total flow resistance of the openings between the twoconcentric exhaust chambers.
 2. The device of claim 1, wherein theopenings between the reaction space and the inner exhaust chamber andthe openings between the two exhaust chambers are arranged in thecorresponding walls along a respective azimuthal ring zone.
 3. Thedevice of claim 1, wherein the openings between the reaction space andthe inner exhaust chamber and the openings from the inner exhaustchamber each have the same dimensions and are arranged at equal spacingswith respect to each other.
 4. The device of claim 1, wherein the numberof the openings between the reaction space and the inner exhaust chamberis larger than the number of openings between the two exhaust chambers.5. The device of claim 3, wherein the individual openings between thereaction space and the inner exhaust chamber are larger than theindividual openings between the two exhaust chambers.
 6. The device ofclaim 1, wherein the total flow resistance for the spent reaction gasbetween the two exhaust chambers is adjusted to be larger by a factor ofat least 5, than the flow resistance between the reaction space and theinner exhaust chamber.
 7. The device of claim 1, wherein the total flowresistance for the spent reaction gas between the two exhaust chambersis adjusted to be larger by a factor of at least 20 to 100, than theflow resistance between the reaction space and the inner exhaustchamber. Pg,11
 8. The device of claim 1, wherein the flow resistance inthe gas venting tube for gas leaving the outer exhaust chamber iscontrollable by a valve and that the flow resitance with the valve openis so small that the total flow resistance is practically set by theflow resistance between the two exhaust chambers.
 9. The device of claim1, wherein the openings between the reaction space and the inner exhaustchamber are horizontal slots which complement each other to form ahorizontal annular slot interrupted only by local spacers between a lidof the reaction vessel and the upper edge of the cylindrical wall of thereaction space.
 10. The device of claim 9, wherein the openings betweenthe reaction space and the inner exhaust chamber are arranged directlyat the upper end of the reaction space.
 11. The device of claim 9,wherein both concentric and annular exhaust chambers are closed on topby a lid on the reaction vessel, said lid extending radially beyond thewall of the reaction vessel.
 12. The device of claim 11, wherein theouter exhaust chamber is formed by two annular walls which extenddownward from the lid of the reaction vessel and are arrangedconcentrically with respect to each other and to the reaction space,said walls being hermetically connected with each other, a gas ventingtube attached at the outer wall and connecting openings in the innerwall connecting to the inner exhaust chamber.
 13. The device of claim12, wherein the wall of the reaction space consists of quartz and thelid of the reaction vessel consists of metal.
 14. The device of claim12, wherein the wall of the reaction space consists of glass and the lidof the reaction vessel consists of alloy steel.
 15. The device of claim12, wherein the walls of the outer exhaust chamber consists of the samematerial as the lid of the reaction vessle.
 16. The device of claim 12,wherein the inner exhaust chamber formed by the inner wall of the outerexhaust chamber and the wall of the reaction space is sealed toward thebottom by a sealing ring of thermally and chamically resistant,resilient material.
 17. The device of claim 16 wherein the sealing ringis pressed by means of a metal washer from the outside against the wallof the reaction space and against the inner wall of the outer exhaustchamber, said washer being tightened against the lower edge of the wallof the outer exhaust chamber by means of a mounting and clamping device.18. The device of claim 1, wherein a quartz glass viewing window isdisposed in the lid of the reaction vessel.